A gear-turbofan engine consists of an epicyclic gear system coupling the turbine to the fan. In this manner, both the fan and the turbine can operate at each component's own optimum speed. The fan and the turbine may be coupled to one another through a gear train that is supported by a journal bearing system.
During powered operation of the engine, lubricant is delivered to the journal bearings by means of one or multiple oil pumps. This lubricant develops a hydrodynamic film at the journal bearing surface between the gear bore and the journal pin shaft in order to minimize wear as these surfaces move with respect to one another. The oil pump(s) pump lubricant from an oil sump and deliver pressurized oil to the journal bearings. At the journal bearings, oil is squeezed by the rotation of the gears and generates a hydrodynamic film which is necessary to prevent undesirable metal-to-metal contact between the gear bore and the journal pin shaft.
During the non-operating condition of the engine, the oil pump(s) stop running. If no lubricant is delivered to the journal bearings, the gear bore is in direct contact with the journal pin shaft under the effect of gravity. Under this circumstance, any relative motion between the gear bore inner surface and the journal pin outer surface can cause premature wear and undesirable damage to these surfaces. An auxiliary oil pump is therefore sometimes provided that is mechanically coupled to the epi-cyclic gear system so that the auxiliary oil pump will rotate with rotation of the engine.
In the engine non-operating mode, rotation of the rotor, and hence the gears, can be caused by wind-milling, a phenomenon resulting from ambient wind blowing through the engine, causing the turbofan engine to rotate due to forces imparted by the wind to engine surfaces. Depending on the wind direction, either toward the fan blade through the nacelle inlet or toward the turbine blade through the exhaust duct, the rotor can rotate in either direction, clockwise or counter-clockwise with respect to the pilot view. Rotation of the rotor during the engine non-operating mode may be caused by other means, such as manual rotation to name just one non-limiting example. Any rotation of the rotor during the engine non-operating mode, no matter what is the cause of the rotation, is referred to herein for convenience as “wind-milling”.
Currently, there are no known means to deliver oil effectively to the journal bearings when the wind-milling phenomenon occurs in both rotational directions. The present disclosure is related to a system and method of supplying lubricant to the journal bearings of a gear-turbofan engine operating with a gear train when the rotor is subjected to a wind-milling condition in both directions, either clockwise or counter-clockwise. The presently disclosed embodiments will also find applicability in other applications where lubrication is to be applied when a gear train is operating in either clockwise or counter-clockwise directions.